Algorithm for real-time process control of electro-polishing

ABSTRACT

Method and apparatus for process control of electro-processes. The method includes electro-processing a wafer by the application of two or more biases and determining an amount of charge removed as a result of each bias, separately. In one embodiment, an endpoint is determined for each bias when the amount of charge removed for a bias substantially equals a respective target charge calculated for the bias.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 10/244,688, filed Sep. 16, 2002, entitled PROCESSCONTROL IN ELECTROCHEMICALLY ASSISTED PLANARIZATION and U.S. patentapplication Ser. No. 10/391,324, filed Mar. 18, 2003, entitled PROCESSCONTROL IN ELECTRO-CHEMICAL MECHANICAL POLISHING, herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to polishing, planarization,plating and combinations thereof. More particularly, the inventionrelates to the monitoring and control of electro-processing, polishingand plating.

2. Description of the Related Art

Sub-quarter micron multi-level metallization is one of the keytechnologies for the next generation of ultra large-scale integration(ULSI). The multilevel interconnects that lie at the heart of thistechnology require planarization of interconnect features formed in highaspect ratio apertures, including contacts, vias, trenches and otherfeatures. Reliable formation of these interconnect features is veryimportant to the success of ULSI and to the continued effort to increasecircuit density and quality on individual wafers and die.

In the fabrication of integrated circuits and other electronic devices,multiple layers of conducting, semiconducting, and dielectric materialsare deposited on or removed from a surface of a wafer. Thin layers ofconducting, semiconducting, and dielectric materials may be deposited bya number of deposition techniques. Common deposition techniques inmodern processing include physical vapor deposition (PVD), also known assputtering, chemical vapor deposition (CVD), plasma-enhanced chemicalvapor deposition (PECVD), and electrochemical plating (ECP).

As layers of materials are sequentially deposited and removed, theuppermost surface of the wafer may become non-planar across its surfaceand require planarization. An example of a non-planar process is thedeposition of copper films with the ECP process in which the coppertopography simply follows the already existing non-planar topography ofthe wafer surface, especially for lines wider than 10 microns.Planarizing a surface, or “polishing” a surface, is a process wherematerial is removed from the surface of the wafer to form a generallyeven, planar surface. Planarization is useful in removing undesiredsurface topography and surface defects, such as rough surfaces,agglomerated materials, crystal lattice damage, scratches, andcontaminated layers or materials. Planarization is also useful informing features on a wafer by removing excess deposited material usedto fill the features and to provide an even surface for subsequentlevels of metallization and processing.

Chemical Mechanical Planarization, or Chemical Mechanical Polishing(CMP), is a common technique used to planarize wafers. CMP utilizes achemical composition, typically a slurry or other fluid medium, forselective removal of materials from wafers. In conventional CMPtechniques, a wafer carrier or polishing head is mounted on a carrierassembly and positioned in contact with a polishing pad in a CMPapparatus. The carrier assembly provides a controllable pressure to thewafer, thereby pressing the wafer against the polishing pad. The pad ismoved relative to the wafer by an external driving force. The CMPapparatus affects polishing or rubbing movements between the surface ofthe wafer and the polishing pad while dispersing a polishing compositionto affect chemical activities and/or mechanical activities andconsequential removal of materials from the surface of the wafer.

Another planarization technique is Electro Chemical Mechanical Polishing(ECMP). ECMP techniques remove conductive materials from a wafer surfaceby electrochemical dissolution while concurrently polishing the waferwith reduced mechanical abrasion compared to conventional CMP processes.The electrochemical dissolution is performed by applying a bias betweena cathode and a wafer surface to remove conductive materials from thewafer surface into a surrounding electrolyte. Typically, the bias isapplied by a ring of conductive contacts to the wafer surface in a wafersupport device, such as a wafer carrier head. Mechanical abrasion isperformed by positioning the wafer in contact with conventionalpolishing pads and providing relative motion there between.

An objective of polishing is to remove a predictable amount of materialto achieve a desired profile. Accordingly, any polishing techniquerequires an endpoint detection to determine when the appropriate amountof material has been removed for various regions of the wafer. However,the progress of the polishing operation is not easily viewable becauseof the contact between the wafer and the pad.

In addition, variations in the polishing conditions impede an accuratedetermination of the polishing endpoint. Variations in theslurry/electrolyte composition, pad condition, relative speed betweenthe pad and the wafer, and the load of the wafer on the pad, etc, causevariations in the material removal rate, which change the time needed toreach the polishing endpoint. Therefore, the polishing endpoint cannotbe estimated merely as a function of polishing time.

One approach to predict the polishing endpoint is to remove the waferfrom the polishing apparatus and measure the thickness of the remainingfilm on the wafer. Doing so periodically during polishing, the quantityof material being removed from the wafer may be determined. As such, alinear approximation of the material removal rate may be used todetermine the polishing endpoint. However, this method is timeconsuming, and does not account for sudden changes in the removal ratethat may occur between measurement intervals.

Several non-invasive methods of endpoint detection are known. One typeof endpoint detection typically requires access to at least a portion ofthe wafer surface being polished, such as by sliding a portion of thewafer over the edge of the polishing pad or through a window in the pad,and simultaneously analyzing the exposed portion of the wafer. Forexample, where polishing is used to expose metal lines embedded in adielectric layer, the overall or composite reflectivity of the surfacebeing polished changes as the lines are exposed. By monitoring thereflectivity of the polished surface or the wavelength of lightreflected from the surface, the exposure of the lines through thedielectric layer, and thus the polishing endpoint, can be detected.However, this method does not provide a way of determining the polishingendpoint unless an underlying layer is exposed during polishing.Additionally, this approach is somewhat erratic in predicting thepolishing endpoint unless all of the underlying lines are simultaneouslyexposed. Furthermore, the detection apparatus is delicate and subject tofrequent breakdown caused by the exposure of the measuring or detectingapparatus to the slurry or electrolytic fluid.

A second type of method for determining the polishing endpoint monitorsvarious process parameters, and indicates an endpoint when one or moreof the parameters abruptly change. For example, the coefficient offriction at the interface of the polishing pad and the wafer is afunction of the surface condition of the wafer. Where an underlyingmaterial different from the film being polished is exposed, thecoefficient of friction will change also. This affects the torquenecessary to provide the desired polishing pad speed. By monitoring thischange, the endpoint may be detected.

In an ideal system, where no parameter other than the wafer surfacechanges, process parameter endpoint detection is acceptable. However, asthe wafer is being polished, the pad condition and theslurry/electrolyte composition at the pad-wafer interface also change.Such changes may mask the exposure of the underlying metal layer, orthey may imitate an endpoint condition, leading to a premature stop ofpolishing.

Finally, ECMP presents a chemically, electrically and physically uniqueenvironment, with respect to conventional CMP. Thus, while the endpointdetection techniques (including those described above) exist for CMP,the techniques may not be readily extendible to ECMP. Even where thetechniques are extendible to ECMP, doing so may require retrofittingexisting processing systems with expensive equipment. A preferredapproach would mitigate or avoid the challenges with retrofittingexisting systems.

Therefore, there is a need for polishing control, and in particularthere is a need for endpoint detection, which accurately and reliablydetermines when to cease polishing during electro-processing.

SUMMARY OF THE INVENTION

In general, embodiments are relating to process control ofelectro-processing. Some aspects of the invention are generally directedto determining removal of material from a wafer during polishing and todetermining an endpoint of a polishing cycle. Other aspects are directedto determining target charge values for a plurality of electrode zones(e.g., two or more) which can be independently biased.

One embodiment provides a method for producing a desired profile on awafer by electro-processing. The method includes determining, for thewafer, a removal profile in order to obtain the desired profile;applying a first bias to the wafer by a first electrode; applying asecond bias to the wafer by a second electrode, the second bias beingdifferent from the first bias; electro-processing the wafer under theinfluence of the first and second bias to selectively change a thicknessof a conductive material of the wafer; determining an amount of chargeremoved from the wafer by each electrode; and terminating theelectro-processing when the desired profile is substantially achievedaccording to the determined amount of charge removed.

Another embodiment provides a method for removing a desired amount ofmaterial from a wafer by electropolishing. The method includesdetermining, for the wafer, a desired removal profile in order to obtaina desired profile; electropolishing the wafer to selectively removedifferent amounts of conductive material from the wafer according to thedesired removal profile; determining an amount of charge removed from aplurality of locations on the wafer; determining a thickness of materialremoved from the wafer for each of the plurality of locations on thebasis of each amount of charge removed at each of the plurality oflocations; and terminating the electropolishing when the desired removalprofile is substantially achieved.

Another embodiment provides a method for determining an endpoint of apolishing cycle for a wafer being processed in a cell body defining anelectrolyte-containing volume, wherein the electrolyte-containing volumecontains at least electrolyte. The method includes providing at least afirst electrode and a second electrode; positioning a wafer in contactwith a polishing pad at least partially submersed in the electrolyte;electropolishing one or more conductive materials on the wafer bybiasing each of the first and second electrodes at different bias levelsto effect different removal rates of material from the wafer; anddetermining whether the endpoint of the polishing cycle for the wafer isreached. In one embodiment the determining includes determining anamount of charge removed from the wafer by each electrode; anddetermining whether each amount of charge removed from the wafer by eachelectrode equals a target charge value for the respective electrode.

Yet another embodiment provides a method of determining removal ofmaterial from a plurality of points on a wafer, the removal beingeffected at least in part by electrochemical activity. The methodincludes determining trajectories for a plurality of points on a waferrelative to a plurality of electrodes each capable of being separatelybiased at different bias levels during electrochemical processing; basedon the trajectories, determining an amount of time each of the pluralityof points spends being affected by each of the electrodes; based on thetrajectories and a predetermined charge-removal relationship relatingcharge removed to amount of material removed from the wafer, determiningan average amount of material removed from the wafer as effected by eachof the electrodes; and for each point of the plurality of points on thewafer, calculating an amount of material removed at the point as the sumof the average amounts of material removed from the wafer as effected byeach of the electrodes weighted by the corresponding amount of timespent being affected by the respective electrode.

Yet another embodiment provides a method of electro-processing a wafer,the method including providing an electrode assembly comprising at leasttwo separately biased electrodes; providing a process model whichrelates a charge for each of the electrodes to an amount of materialremoved at each of a plurality of points on a wafer on the basis of apredetermined trajectory of the plurality of points relative to theelectrodes and a predetermined charge-removal relationship which relatescharge removed to amount of material removed from the wafer; for aspecified desired profile of the wafer, determining a target charge foreach electrode according to the process model; moving the wafer relativeto the electrodes according to the predetermined trajectory of theplurality of points; and terminating each bias to the respectiveelectrode upon reaching the respective target charge.

Still another embodiment provides a computer readable medium containinga program which, when executed, performs an operation during anelectropolishing process occurring for a wafer in contact with apolishing pad at least partially submersed in electrolyte. The operationincludes applying a first bias to the wafer by a first electrode;applying a second bias to the wafer by a second electrode, the secondbias being different from the first bias; electro-processing the waferunder the influence of the first and second bias to selectively change athickness of a conductive material of the wafer; determining an amountof charge removed from the wafer by each electrode; and terminating theelectro-processing when a desired profile is substantially achievedaccording to the determined amount of charge removed.

Still another embodiment provides an electro-processing system includinga cell body defining an electrolyte-containing volume; an electrodeassembly comprising at least two electrodes; at least two correspondingpower supplies each electrically connected to one of the at least twoelectrodes to separately bias the respective electrode; a chargedetermination unit configured to at least periodically determine anamount of charge removed from the wafer by each of the electrodes basedon the current supplied to each of the electrodes over time; and aprocess control unit configured to detect an endpoint for each of theelectrodes, separately, based on whether the amount of charge removed bya given electrode equals a calculated target charge for the givenelectrode.

Still another embodiment provides an electro-processing system includinga cell body defining an electrolyte-containing volume; an electrodeassembly comprising at least two electrodes; at least two correspondingpower supplies each electrically connected to one of the at least twoelectrodes to separately bias the respective electrode; a chargedetermination unit configured to at least periodically determine anamount of charge removed from the wafer by each of the electrodes basedon the current supplied to each of the electrodes over time; and aprocess control unit configured to determine when a desired profile issubstantially achieved according to the determined amount of chargeremoved by each of the electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited embodiments are attainedand can be understood in detail, a more particular description may behad by reference to the appended drawings. It is to be noted, however,that the appended drawings illustrate only typical embodiments of thisinvention and are therefore not to be considered limiting of its scope,for the invention may admit to other equally effective embodiments.

FIG. 1 is a perspective view of one embodiment of a processingenvironment having a profile measurement station, an electro-processingplatform and a computer for controlling processes performed on theplatform.

FIG. 2 is a side cross-sectional view of an electro-polishing station.

FIG. 3 is a top view of one embodiment of a polishing pad having contactelements disposed therein.

FIG. 4 is top view of one embodiment of an electrode assembly defining aplurality of zones.

FIG. 5 is a side cross-sectional, exploded view of a polishing assemblywhich includes the polishing pad of FIG. 3 and the electrode assembly ofFIG. 4.

FIG. 6 is a block diagram of a process control unit configured forprocess monitoring and endpoint detection based on charge removed byvarious zones of the electrode assembly of FIG. 4.

FIGS. 7-10 are graphs illustrating removal profiles for various chargevalues.

FIG. 11 shows one example of an empirically determined curve relatingtotal charge and material removed.

FIGS. 12-13 are top perspective views of a substrate having a materiallayer thereon, wherein the material layer may be polished in order todevelop a relationship between removal and charge.

FIG. 14 are representative traces of wafer point trajectories relativeto electrode zones.

FIG. 15 are representative curves illustrating the percent of timevarious points on a wafer spent in three separate electrode zones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides systems and methods forelectro-processing wafers. Generally, electro-processing is performed toremove or deposit material on the wafer. Embodiments are provided fordetermining a profile for a wafer, calculating charge values anddetecting an endpoint of an electro-processing cycle. In one embodiment,an electro-processing system is provided with a plurality of powersupplies each connected to a different zone of an electrode. The powersupplies are independently controlled to provide a desiredvoltage/current signal to a respective zone. The current is monitoredand related to the total removal/deposition of material from a wafer todetermine the end point of the process.

The words and phrases used herein should be given their ordinary andcustomary meaning in the art by one skilled in the art unless otherwisefurther defined. A wafer refers to a workpiece which is typicallydisc-shaped, but my be otherwise (e.g., square). The wafer is typicallya substrate having one or more layers formed thereon, at least one ofwhich is conductive (typically the upper-most layer). The layer(s) ofthe wafer may or may not be patterned. Chemical-mechanical polishingshould be broadly construed and includes, but is not limited to,abrading a wafer surface (e.g., an upper-most conductive layer) bychemical activities, mechanical activities, or a combination of bothchemical and mechanical activities. Electro-processing refers to anyprocess using electrical activity to remove or deposit material on awafer. Particular examples of electro-processing for removing materialfrom a wafer include electro-polishing, electrochemical mechanicalpolishing, and electrochemical mechanical plating process.Electro-polishing should be broadly construed and includes, but is notlimited to, planarizing a wafer by the application of electrical and/orelectrochemical activity and a particular example includeselectrochemical mechanical polishing. Electrochemical mechanicalpolishing (ECMP) should be broadly construed and includes, but is notlimited to, planarizing a wafer by the application of electrochemicalactivity, mechanical activity, or a combination of both electrochemicaland mechanical activity to remove materials from a wafer surface.Electrochemical mechanical plating process (ECMPP) should be broadlyconstrued and includes, but is not limited to, electrochemicallydepositing material on a wafer and concurrently planarizing thedeposited material by the application of electrochemical activity,mechanical activity, or a combination of both electrochemical andmechanical activity.

Embodiments of the invention broadly provide for real-time removalmonitoring and endpoint detection in a electro-processing system. Ingeneral, any of the above-defined techniques may be used, individuallyor in combination. Further, it is contemplated that polishing andplating may occur simultaneously or alternately. The foregoingembodiments are broadly, collectively characterized aselectro-processing. While embodiments are described primarily withreference to a form of electro-polishing, it is understood that theinvention is not so limited. Rather, embodiments include any form of theelectro-processing. Thus, any reference to particular embodiments ofelectro-polishing are merely for purposes of illustration.

FIG. 1 depicts wafer processing environment 100. The processingenvironment 100 includes a profile measurement station 102, anelectrochemical mechanical polishing (ECMP) platform 104, a computer 106and a plurality of power supplies 108A, 108B, . . . 108N (collectivelyreferred to as the power supplies 108). The profile measurement station102 is generally any device or devices configured to measure profiles ofwafers. Exemplary non-contact devices which may be used include iScanand iMap, which scan and map the wafer, respectively. In theillustrative embodiment of FIG. 1, the profile measurement station 102represents an ex-situ device; that is, profile measurement is performedat a location different from where polishing is performed. However, insitu profile measurement (e.g., on the polishing platform 104) is alsocontemplated. In either case, the profile measurement station 102measures a profile of a wafer (referred to as the “initial profile”) andprovides this measurement to the computer 106.

The polishing platform 104 may be any apparatus adapted for polishingwafers by electro-processes. One polishing platform that may be adaptedto benefit from the invention is a REFLEXTION® chemical mechanicalpolisher available from Applied Materials, Inc. located in Santa Clara,Calif.

Illustratively, the polishing platform 104 includes a plurality ofpolishing stations 110A-C. By way of example three polishing stations(P1, P2, P3) are shown. More generally, the polishing platform 104 mayinclude any number of polishing stations (i.e., one or more). Thepolishing platform 104 may also include other process stations, such asrinse stations.

The processes performed on wafers by the polishing platform 104 aregenerally controlled by the computer 106. The computer 106 may berepresentative of, or include, any programmable device configured tocarry out embodiments of the invention. Thus, in one embodiment, thecomputer 106 is representative of a controller or a plurality ofcontrollers configured with code which, when executed, performspolishing operations. In other embodiments, the computer 106 may becharacterized as a client computer, a server computer, a portablecomputer, an embedded controller, a PC-based server, a minicomputer, amidrange computer, a mainframe computer, and other computers adapted tosupport the methods, apparatus, and article of manufacture of theinvention.

To implement desired polishing processes the computer 106 is configuredwith a process control unit 112. In one embodiment, the process controlunit 112 is implemented in software, but may also be implemented inhardware. In either case, the code of the process control unit 112defines functions of the preferred embodiment and can be contained on avariety of signal-bearing media (or computer readable media). The code(or the instructions implemented by such code) includes, but is notlimited to, (i) information permanently stored on non-writable storagemedia, (e.g., read-only memory devices within a computer such as CD-ROMdisks readable by a CD-ROM drive); (ii) alterable information stored onwritable storage media (e.g., floppy disks within a diskette drive orhard-disk drive); or (iii) information conveyed to a computer by acommunications medium, such as through a computer or telephone network,including wireless communications. The latter embodiment specificallyincludes information downloaded from the Internet and other networks.Such signal-bearing media, when carrying computer-readable instructionsthat direct the functions of the present invention, representembodiments of the present invention.

In various embodiments, the process control unit 112 is capable ofprofile determination, real-time process monitoring and end pointdetection. These functions may be performed on the basis of variousinput, including the initial profile received from the profilemeasurement station 102. The process control unit 112 then causes thecomputer 106 to issue control signals 114 to each of the power supplies108. In response to the control signals 114, the power supplies 108 eachissue a separate electrical signal, collectively referred to as theelectrical signals 116. Each of the electrical signals 116 provides acurrent/voltage to a separate one of a plurality of same-polarityelectrodes (e.g., two or more) of a given one of the polishing stations110A-C. The individual electrodes receiving the control signals 114 arealso referred to herein as “zones” of a single electrode. Accordingly,in one embodiment, each electrode/zone has an associated one of thepower supplies 108. It is noted, however, that while separate powersupplies may be used, a single unit capable of producing multipleelectrical signals of different voltage/current may also be used.Therefore, the term “power supplies” as used herein does not necessarilydenote physically separate power supplies. Also, the number of powersupplies and respective electrodes/zones may be varied.

In one embodiment, during processing of a given wafer on one of thepolishing stations 110A-C, removal of material from the wafer ismeasured as charge. In one embodiment, charge is calculated byintegrating current with respect to time. As such, each of the powersupplies 108 may be configured with an integration unit 118 whichintegrates the current being provided by the respective power supply toelectrode/zone of the polishing station. The output 120 (i.e., thecharge per electrode/zone) of the integration units 118 is provided tothe process control unit 112. Although shown as part of the powersupplies 108, the integration units 118 may alternatively be part of theprocess control unit 112, or be separate units altogether. Each of theforegoing aspects will be described in more detail below.

Referring now FIG. 2, one embodiment of a process cell 200 is shown inside cross-section. The process cell 200 may be representative of a celllocated at any one or all of the polishing stations 110A-C shown inFIG. 1. In particular, the polishing station 200 is a “face-down”polishing apparatus. However, embodiments using “face-up” polishingapparatus are also contemplated.

The process cell 200 generally includes a basin 204 and a polishing head202. A substrate 208 is retained in the polishing head 202 and loweredinto the basin 204 during processing in a face-down (e.g., backside up)orientation. An electrolyte is flowed into the basin 204 and in contactwith the substrate's surface while the polishing head 202 places thesubstrate 208 in contact with a polishing article 203. In oneembodiment, the substrate 208 and the polishing article 203 disposed inthe basin 204 are moved relative to each other to provide a polishingmotion (or motion that enhances plating uniformity). The polishingmotion generally comprises at least one motion defined by an orbital,rotary, linear or curvilinear (e.g., sweep) motion, or combinationsthereof, among other motions. The polishing motion may be achieved bymoving either or both of the polishing head 202 and the basin 204. Thepolishing head 202 may be stationary or driven to provide at least aportion of the relative motion between the basin 204 and the substrate208 held by the polishing head 202. In the embodiment depicted in FIG.2, the polishing head 202 is coupled to a drive system 210. The drivesystem 210 moves the polishing head 202 with orbital, rotary, linear, orcurvilinear (e.g., sweep) motions, or combinations thereof.

The polishing head 202 generally retains the substrate 208 duringprocessing. In one embodiment, the polishing head 202 includes a housing214 enclosing a bladder 216. The bladder 216 may be deflated whencontacting the substrate to create a vacuum therebetween, thus securingthe substrate to the polishing head 202. The bladder 216 mayadditionally be inflated to press the substrate in contact with thepolishing article 203. A retaining ring 238 is coupled to the housing214 and circumscribes the substrate 208 to prevent the substrate fromslipping out from the polishing head 202 while processing. One polishinghead that may be adapted to benefit from the invention is a TITAN HEAD™carrier head available from Applied Materials, Inc., located in SantaClara, Calif.

The basin 204 is generally fabricated from a plastic such asfluoropolymers, TEFLON® polymers, perfluoroalkoxy resin, PFA,polyethylene-based plastics, PE, sulfonated polyphenylether sulfones,PES, or other materials that are compatible or non-reactive withelectrolyte compositions that may be used in electroplating orelectropolishing. The basin 204 includes a bottom 244 and sidewalls 246.The sidewalls 246 of the basin 204 include a port 218 formedtherethrough to allow removal of electrolyte from the basin 204. Theport 218 is coupled to a valve 220 to selectively drain or retain theelectrolyte in the basin 204.

The basin 204 is rotationally supported above a base 206 by bearings234. A drive system 236 is coupled to the basin 204 and rotates thebasin 204 during processing. A catch basin 228 is disposed on the base206 and circumscribes the basin 204 to collect processing fluids, suchas an electrolyte, that flow out of port 218 disposed through the basin204 during and/or after processing.

The basin 204 defines housing for the polishing article 203 and anelectrode assembly 209 which is disposed between the bottom 244 and thepolishing article 203. In one embodiment, the polishing article 203 andthe electrode 209 may be secured together forming a unitary body thatfacilitates removal and replacement. In embodiment, the polishingarticle 203 and the electrode 209 secured to one another by permanentmeans such as bonding. Alternatively, the polishing article 203 and theelectrode 209 may be coupled by other techniques or combination thereof,including sewing, binding, heat staking, riveting, screwing and clampingamong others. In still another embodiment the polishing article 203 issecured to a belt assembly which dispenses new (i.e., clean) padmaterial and takes up old (i.e., worn or contaminated) pad material.

As will be described in more detail with reference to FIG. 5, theelectrode assembly 209 generally includes a plurality (e.g., at leasttwo) of electrodes or zones. Each electrode is coupled to a lead 212A ofone of the power supplies 108. The other lead 212B of each of the powersupplies 108 is coupled to the polishing article 203, which is itself anelectrode. For simplicity only one set of leads (positive and negative)is shown. Illustratively, the leads 212A-B are routed through a slipring 226 disposed below the basin 204. The slip ring 226 facilitatescontinuous electrical connection between the power supplies 108 and thepolishing article and electrode assembly 209 as the basin 204 rotates.The leads 212A-B may be wires, tapes or other conductors compatible withprocess fluids or having a covering or coating that protects the leads212A-B from the process fluids. Examples of materials that may beutilized in the leads 212A-B include insulated copper, graphite,titanium, platinum, gold, and HASTELOY®) materials among othermaterials. Coatings disposed around the leads 212A-B may includepolymers such as fluorocarbons, PVC, polyamide, and the like.

In order to operate as electrode, the polishing article 203 is made atleast partially conductive by the provision of conductive materialdisposed in the polishing article 203. In general, the base material ofthe polishing article 203 may itself be made conductive, or conductiveelements may be disposed in a non-conductive base material such aspolyurethane. Particular embodiments of the polishing article 203 aredescribed below.

In one embodiment, the electrode assembly 209 communicates electricallywith the substrate 208 via perforations 205 formed in the polishingarticle 203. Thus, in one embodiment, the ability of the electrodeassembly 209 to affect electro-processing is determined, in part, by thepresence and location of the perforations 205. Specifically, it iscontemplated that, in at least one embodiment, electro-processing iseffected substantially only in those locations of the wafer 208“visible” to the electrode assembly 209 through the perforations 205.Relatedly, it is contemplated that the proximity of the electrodeassembly 209 to the wafer 208 affects processing. Generally, a closerproximity is preferred. Accordingly, in the illustrative embodiment ofFIG. 2, the electrode assembly 209 is shown directly interfacing withthe polishing article 203. However, the provision of intermediatematerials between the electrode assembly 209 and the polishing article203 is also contemplated.

An electrolyte delivery system 232 is generally disposed adjacent thebasin 204. The electrolyte delivery system 232 includes a nozzle oroutlet 230 coupled to an electrolyte source 242. The outlet 230 flowselectrolyte or other processing fluid from the electrolyte source 242 tointo the basin 204. During processing, the electrolyte generallyprovides an electrical path for biasing the substrate 208 and driving anelectro-chemical process to remove and/or deposit material on thesubstrate 208. Alternatively, the electrolyte delivery system mayprovide electrolyte through the bottom 244 of the process cell and flowelectrolyte through the electrode assembly 209 and the perforations 205of the polishing article 203 into contact with the substrate 208.

In operation, electrolyte is flowed into the basin 204 from theelectrolyte delivery system 232. The electrolyte fills the basin 204 andis thus brought into contact with the wafer 208 and polishing article203. To initiate electrochemical mechanical processing, potentialdifferences are applied between the electrode assembly 209 and theconductive portion of the polishing article 203. The wafer 208 being indirect contact with the conductive portion of the polishing article 203will then be at the same potential as the conductive portion. Thecurrent loop is then completed in the polishing station by transformingatomic wafer materials into ions in the electrolyte. Concurrentmechanical polishing of the wafer 208 is achieved by relative movementbetween the wafer and the polishing article 203. In one embodiment,polishing continues until reaching an endpoint, as determined by theprocess control unit 112. In at least one embodiment, “endpoint” refersto a point in time during a polishing cycle at which sufficient bulkmetal has been removed from a wafer. Following detection of theendpoint, it may be necessary to continue polishing for a period of timein order to remove residual metal.

As noted above, the polishing article 203 is at least partiallyconductive. The conductivity of the polishing article may beaccomplished in a variety of ways. Referring now to FIG. 3, oneembodiment of the polishing article 203 is shown. In general, thepolishing article 203 is a disk-shaped polishing pad 302 having aplurality of conductive elements 304 disposed thereon. For simplicityand clarity, the perforations 205 described above with reference to FIG.2 are not shown. The polishing pad 302 may be made of polymericmaterials, such as polyurethane, polycarbonate, polyphenylene sulfide(PPS), or combinations thereof, and other polishing materials used inpolishing wafer surfaces. An exemplary conventional material includesthose found in the IC series of polishing media, for examplepolyurethane and polyurethane mixed with fillers, commercially availablefrom Rodel Inc., of Phoenix, Ariz. The invention further contemplatesthe use of other conventional polishing materials, such as a layer ofcompressible material. The compressible material may include aconventional soft material, such as compressed felt fibers leached withurethane. Further, the use of abrasive materials embedded in thepolishing pad is contemplated. The fixed abrasive particles may includeconductive abrasive materials and/or nonconductive abrasive materials.

The conductive elements 304 are shown disposed in a symmetrical patternat a central region of the polishing pad 302. The pattern shown in FIG.3 is merely illustrative and other patterns may be used. In addition,the number of conductive elements 304 may be varied. In one embodiment,the conductive elements 304 are rigidly fixed in place. In anotherembodiment, the conductive elements 304 are rotatably disposed relativeto the polishing pad 302 so that the conductive elements 304 may rotateover the surface of a wafer brought into contact with the conductiveelements 304. A variety of embodiments are described in U.S. patentapplication Ser. No. 10/210,972, filed Aug. 2, 2002, entitled CONTACTSFOR ELECTROCHEMICAL PROCESSING, herein incorporated by reference in itsentirety.

Alternatively or additionally, the polishing article 203 is madeconductive by making the polishing material itself of conductivematerial. The conductive polishing material may include conductivepolymers, polymer composites with conductive materials, conductivemetals, conductive fillers or conductive doping materials, orcombinations thereof. Conductive polymers include polymeric materialsthat are intrinsically conductive, such as polyacetylene,polyethylenedioxythiophene (PEDT), polyaniline, polypyrrole, andcombinations thereof. The polymer composites with conductive materialsmay include polymer-noble metal hybrid materials. Polymer-noble metalhybrid materials that may be used as the conductive polishing materialdescribed herein are preferably chemically inert with a surroundingelectrolyte, such as those with noble metals that are resistant tooxidation. An example of a polymer-noble metal hybrid material is aplatinum-polymer hybrid material. The invention also contemplates theuse of polymer-noble metal hybrid materials, which are chemicallyreactive with a surrounding electrolyte, when the polymer-noble metalhybrid material is insulated from a surrounding electrolyte by anothermaterial. Conductive metals that may be used as the polishing materialare those metals that are preferably relatively inert to chemicalreactions with the surrounding electrolyte. Platinum is an example of aconductive metal that may be used as the polishing material. Theconductive metals may form a portion or the entire polishing surface ofthe polishing material. When forming a portion of the polishing surface,the conductive metals are typically disposed in a conventional polishingmaterial.

The conductive polishing materials may further include conductivefillers or conductive doping materials disposed in a binder material,such as the conductive polymers described above or a conventionalpolishing material. Examples of conductive fillers include carbonpowder, carbon fibers, carbon nanotubes, carbon nanofoam, carbonaerogels, and combinations thereof. Carbon nanotubes are conductivehollow filaments of carbon material having a diameter in the nanometersize range. The conductive fillers or conductive doping materials aredisposed in the binding material in an amount sufficient to provide apolishing medium having a desired conductivity. The binder material istypically a conventional polishing material.

Alternatively or additionally, the polishing article 203 may comprise ametal mesh disposed in the polishing material. The metal mesh maycomprise a chemically inert conductive material, such as platinum. Themetal mesh may also include materials that have been observed to reactwith the surrounding electrolyte, such as copper, if the metal mesh ischemically insulated from the electrolyte such as by a conformal layerof conventional material.

Other embodiments of conductive polishing pads which may be used toadvantage are further described in U.S. patent applications Ser. No.10/033,732, filed Dec. 27, 2001, entitled CONDUCTIVE POLISHING ARTICLEFOR ELECTROCHEMICAL MECHANICAL POLISHING and Ser. No. 10/140,010, filedMay 7, 2002, entitled CONDUCTIVE POLISHING ARTICLE FOR ELECTROCHEMICALMECHANICAL POLISHING, each of which is hereby incorporated by referencein their entireties.

In any case, where the polishing article 203 is at least partiallyconductive, the polishing article 203 acts as an electrode incombination with a wafer during electro-processes. The electrodeassembly 209 provides plurality of counter-electrodes to the polishingarticle 203. One embodiment of the electrode assembly 209 is shown inFIG. 4, now described.

FIG. 4 shows a top view of the electrode assembly 209. The electrodeassembly 209 generally includes a plurality of electrodes. Specifically,four electrodes 402A-D (collectively, electrodes 402) are shown,although the electrode assembly 209 may include any number ofelectrodes. Illustratively, the electrodes 402 are annular members. Inparticular, an innermost electrode 402A is a disk, while the otherelectrodes 402B-D are rings. However, the electrodes may more generallybe any geometry. Further, the electrodes 402 are conductive member madeof, for example, a metal. For electrochemical removal processes, such asanodic dissolution, the electrodes 402 may include a non-consumablematerial other than the deposited material, such as platinum for copperdissolution. However, the electrodes 402 can also be made of copper forcopper polishing, if preferred. Anodic dissolution should be broadlyconstrued and includes, but is not limited to, the application of ananodic bias to a wafer directly or indirectly which results in theremoval of conductive material from a wafer surface and into asurrounding electrolyte solution.

It is noted that for simplicity some features of embodiments of theelectrode assembly 209 are not shown. For example, in one embodiment,the contact elements 304 are disposed through the innermost electrode402A. The openings to receive the contact elements 304 are not shown inFIG. 4. The electrodes are separated from one another by annular gaps404A-D (collectively, gaps 404). In one embodiment, insulating materialmay be disposed in the annular gaps 404. In illustrative configuration,each electrode 402 defines a zone, which can be separately biased byrespective power supply 108. Additional aspects in this regard may bedescribed with reference to FIG. 5.

FIG. 5 shows a side cross-sectional exploded view of the electrodeassembly 209 and the polishing article 203. For purposes of illustrationthe polishing head 202 is also shown carrying a wafer positioned incontact with the upper polishing surface of the polishing pad 302. Tofacilitate illustration, the individual electrodes 402 of the electrodeassembly 209 are shown exploded relative to the polishing pad 302 andrelative to one another (i.e., the size of the gaps 404 betweenelectrodes 402 have been exaggerated). FIG. 5 shows a representativeconfiguration of three power supplies 108A-C with respect to theelectrodes 402. In general, the individual electrodes 402 of theelectrode assembly 209 may be anodes or cathodes depending upon thepositive bias (anode) or negative bias (cathode) applied between theelectrodes 402 and the polishing article 203. For example, depositingmaterial from an electrolyte on the wafer surface, the electrodes 402act as anodes and the wafer surface and/or polishing article 203 acts asa cathode. When removing material from the wafer 208, such as bydissolution from an applied bias, the electrodes 402 function as acathode and the wafer surface and/or polishing article 203 may act as ananode for the dissolution process. In the illustrated embodiment, theelectrodes 402 are connected to the negative leads 512A of the powersupplies 108A-C, while the positive lead 512B are connected to thecontact elements 304. (While the positive lead 512B is shown connectedto only one of the contact elements 304 for simplicity, is understoodthat each of the contact elements 304 may be commonly connected to thepositive lead 512B.) The embodiment of FIG. 5 illustrates that two ormore electrodes 402 may be connected to the same power supply, andtherefore be maintained at the same bias during processing. In thepresent illustration, the innermost electrode 402A and the outer, middleelectrode 402C are connected to the same power supply 108A, while theinner, middle electrode 402B and the outer electrode 402D are connectedto their own respective power supplies 108B and 108C, respectively. Inthis respect, the four member electrode assembly 209 may be considered athree zone assembly.

Referring now to FIG. 6, one embodiment of the process control unit 112is shown. Generally, the process control unit 112 includes a processmodel 602 and a control algorithm 604. In general, the process model 602describes a process environment. In operation, the process model 602receives various model inputs 606. Based on the various model inputs606, the process model 602 generates a target charge value for each zonedefined by the electrode assembly 209 (the target charge values arecollectively shown in FIG. 6 as the target charge values 618). In oneembodiment, the model inputs 606 include a desired removal profile 608,a charge-removal relationship 610 and operations/cell parameters 612.The desired removal profile 608 describes a profile of the material tobe removed from a wafer. In one embodiment, the desired removal profileis the simple arithmetic difference between a measured profile 614(e.g., measured by the profile measurement station 102 shown in FIG. 1)and a desired profile 616, which may be user selected. Thecharge-removal relationship 610 describes a relationship between theamount of charge removed from a wafer and the thickness of materialremoved. The charge-removal relationship 610 is particular to a processand wafer type. Thus, a plurality of such relationships may be stored ina storage device and retrieved as needed. The operations/cell parameters612 describe various aspects of the manner in which a wafer is processedand the cell in which the wafer is being processed and which may have animpact on the resulting removal profile of the wafer. Illustrativeoperations/cell parameters 612 include process parameters, electrodegeometry, and polishing article construction. Process parameters mayinclude, for example, platen rotation speed (i.e., rotation of the basin204 in FIG. 2), head rotation speed (i.e., rotation speed of thepolishing head 202 in FIG. 2), and sweep range and frequency. “Sweep”refers to the translation motion of the head along a radius of theplaten (i.e., the bottom of the basin 204. With reference toconstruction of the electrode assembly 209 of FIG. 4, for example,electrode geometry refers to the geometry of the various electrodes 402which make up the electrode assembly 209. Parameters pertaining to thepolishing article construction include, for example, the geometry of thepolishing pad (such as the polishing pad 302 shown in FIG. 3) and theplacement of the contact elements (such as the contact elements 304shown in FIG. 3). Additional aspects of the process model 602 and itsinputs will be described in more detail below.

The target charge values 618 calculated by the process model 602 areprovided as input to the control algorithm 604. In one embodiment, thecontrol algorithm 604 receives additional control inputs 620, which maybe operator selected. Illustrative control inputs include the totalprocess time, the number of process steps and the like. The controlalgorithm 604 then generates a control signal (collectively, controlsignals 114) for each zone defined by the electrode assembly 209. Thecontrol signals 114 are provided to the respective one of the powersupplies 108. The control signals 114 may be configured to, for example,control current or voltage for the respective zone. Accordingly, thepower supplies 108 produce corresponding electrical signals 622 for therespective zones. In addition, the charge removed per zone is calculatedby each integration unit 118 of the power supplies 108. The calculatedcharge per zone values 624 are fed back to the control algorithm 604.The control algorithm 604 then compares the calculated charge per zonevalues 624 to the respective target charge values 618. That is, thecontrol algorithm 604 compares a calculated charge value for aparticular zone to the corresponding target charge value for that zone.When the calculated charge value exceeds the corresponding target chargevalue, the bias for that zone is terminated. When each of the biases hasbeen terminated, the electro-process is complete. Thus, in one aspect,the process control unit 112 provides for endpoint detection. In anotheraspect, the calculated charge values for each zone can be used togenerate and display the profile of a wafer in real time.

It is noted that the control algorithm 604 can implement the controlsignals 114 according to any variety of functions depending, at least inpart, on the control inputs 620. In one embodiment, the voltage in eachzone is fixed. The voltage in each zone is then independently terminatedonce the target charge is achieved. The voltage in each zone may beselected according to parameters which include removal rate,planarization capability, surface roughness, defect count, etc. Inanother embodiment, the polishing time is fixed. In this case, thevoltage for each zone is modulated (i.e. changed with respect to time)so that the target charge is met for each zone when the predefinedpolishing time expires. While the former embodiment provides simplicity,the latter embodiment allows better control of the step time. In someembodiments, a zone voltage may be zero or negative, while othercontemporaneous zone voltages are positive. It is also contemplated thatthe voltages may be applied prior to any mechanical polishing, duringmechanical polishing and/or after mechanical polishing. Persons skilledin the art will recognize other embodiments.

By way of example only, FIGS. 7-10 show illustrative incoming profiles700, 800, 900, and 1000, respectively. The profiles are plotted on anx-y graph, where the x-axis is the wafer radius in inches and the y-axisis thickness in angstroms. The removal profiles should match theseprofiles in order to achieve the desired target profile. The chargevalues for each of the removal profiles are given in correspondingtables 702, 802, 902 and 1002. In particular, charge values are givenfor an outer zone, a middle zone and a center zone. The cathode geometryused was substantially similar to that shown in FIG. 4, in which zone 1(defined by the innermost electrode 402A) and zone 3 (defined by theouter middle electrode 402C) were held at the same voltage. Accordingly,zone 1 and zone 3 are collectively referred to in FIGS. 7-10 as the“middle” zone. The “outer” zone corresponds to zone 4 and the “center”zone corresponds to zone 2 of the electrode assembly 209 shown in FIG.4.

Charge-Removal Relationship

As noted above, the process model 602 receives as an input acharge-removal relationship. In one embodiment, the charge-removalrelationship is determined empirically, by periodically measuring (e.g.,by sheet resistance measurements) the amount of material removed from awafer being polished. Alternatively, the current may be measured for aseries of wafers processed at different conditions (e.g., slightlydifferent polishing times, voltage biases, etc.). In this manner, acalibration curve can be acquired. One such calibration curve 1100 isshown in FIG. 11. In this case, 9 wafers (1 per data point and 3 perzone in a three-zone electrode arrangement) were polished underdifferent conditions and the average current was recorded. Thethicknesses of the wafers were measured before and after the polishingcycle to determine the average amount of material removed. Thecalibration curve (expressed as y=348.7x+192.35) exhibits a linearrelationship between the Removal (given in angstroms and shown on they-axis) and the Charge (given in amperes*minutes and shown on thex-axis) and allows for the prediction (by extrapolation) of removal fora given current. Additional embodiments for determining such arelationship are described in U.S. patent application Ser. No.10/391,324, filed Mar. 18, 2003, entitled PROCESS CONTROL INELECTRO-CHEMICAL MECHANICAL POLISHING, which is hereby incorporated byreference in its entirety, to the extent not inconsistent with thepresent embodiments.

In a particular embodiment, a charge-removal relationship may bedetermined by polishing a plurality of test material layers using aprocess cell such as the process cell 200 of FIG. 2. The test materiallayers may be polished according to a specific set of instructions thatmay include a relative motion between a polishing pad and a wafer. Therelative motion may be, for example, linear, curvilinear, rotational,orbital, or combinations thereof. A test-bias, V_(t) is then appliedbetween the test material layer and the counter electrodes of theelectrode assembly 209. The test bias, V_(t), may be applied such that asubstantially uniform potential is generated across the counterelectrodes with respect to the surface to be polished. The bias may beapplied to the test material layer using, for example, a pad such as thepad 302 described above in FIG. 3.

Referring now to FIG. 12, a top perspective view of a substrate 1204shows a first test material layer 1205 formed thereon. Similarly, FIG.13 shows a second substrate 1304 having a second test material layer1305 formed thereon. The first test material layer 1205 is polished byapplying a first test bias such as a uniform test bias across the testmaterial layer 1205 relative to the counter electrodes of the electrodeassembly 209.

After polishing the test material layer 1205 for a pre-determined periodof time (a first polishing time), the substrate 1204 is, for example,removed from the process cell 100 and an amount of material removed fromthe test material layer 1205 is then measured. The amount of materialremoved may be determined, for example, using conventional methods ofmeasuring layer thicknesses, such as sheet resistance (Rs) measurements.Alternatively, the amount of material removed may be measured usingelectron microscopy, or similar methods for analyzing thickness andcomposition of material layers. The material removal may be determinedby measuring a thickness 1280 of the test material layer 1205 beforepolishing and the thickness 1280 after polishing. The thickness 1280 maybe measured at a first point 1220. Additional thickness measurements ofthe first test material layer 1205 may be taken at one or moreadditional points 122 in order to obtain a statistically representativevalue for material removal. Alternatively, a property other thanthickness may be measured. For example, a mass of material removed or amaterial removal rate may be measured directly or indirectly. The one ormore additional points 1222 on the test material layer 1205 may bechosen such that the points lie within a region or zone of the testmaterial layer 1205 that experiences a relatively uniform rate ofpolishing (material removal). For example, the first point 1220 and theadditional points 122 may be chosen such that they all lie in anintermediate region 1216 of the test material layer 1205. Alternatively,the first point 1220 and the additional points 122 may be chosen suchthat they each are a distance from a center 1230 of the test materiallayer 1205 that is substantially the same. A first rate of materialremoval may be determined by, for example, dividing mass or thickness ofthe material removed by the first polishing time.

The second test material layer 1305 may be polished using the samegeometry and configuration of the process cell as for the polishing ofthe first test material layer 1205. The second test material layer 1305may be polished to a thickness 1380 by applying a second bias applied tothe second test material layer 1305. Thereafter, the step of determiningmaterial removal may be performed for one or more points 1320 on thesecond test material layer 1305. Furthermore, the process of determiningremoval rate may be repeated for additional test material layers (notshown), if desired.

The one or more points 1320 on the test material layer 1305 may lie, forexample, within an intermediate region 1316. The intermediate region1316 may have a similar shape and define a similar range of distancesfrom a center 1330 of the material layer 1305 as is defined by theintermediate region 1216 with respect to the center 1230.

By matching the material removal from each test material layer 1205,1305 with the corresponding charge (current integrated over time)removed from the test material layer, a relationship between materialremoved and charge may be determined. The relationship thus determinedmay be relevant for a specific configuration of the process cell,including a specific polishing composition as well as specificcomposition of material layer. The relationship may be a linearrelationship, an exponential relationship, or any other relationship.Further, it is recognized that blanket wafers will exhibit a differentcharge-removal relationship than patterned wafers.

Trajectory Simulation

As noted above, the process model 602 also receives as input,operations/cell parameters 612, which may include process parameters,electrode geometry (i.e., the geometry of the various electrodes 402which make up the electrode assembly 209 as illustrated in FIG. 4), andpolishing article construction. In general, the operations/cellparameters 612 are those parameters necessary to simulate a trajectoryof points on a wafer. For each point of the wafer, the amount of timeaffected by each of the electrodes of the electrode assembly 209 can becalculated. In one aspect, a point is affected by an electrode while indirect facing relationship with the electrode via a perforation in thepolishing pad (e.g., one of the perforations 205 of the polishing pad203 shown in FIG. 2. However, the presence of a contact element on thepolishing pad (e.g. one of the contact element 304 shown in FIG. 3) mayinterfere with the interaction between electrode/zone and the point onthe wafer. Hence, a point is considered to be affected by an electrodewhen the electrode is “visible” from the perspective of the point via aperforation.

Referring now to FIG. 14, one illustration of simulated pointtrajectories is shown. Specifically, FIG. 14 shows the electrodeassembly 209 FIG. 4 and three traces that represent the trajectories ofthree separate points on a wafer. Only three points are shown forsimplicity. In practice, however, the trajectories for a plurality ofpoints would be measured. A first trace 1402 corresponds to a centerpoint on the wafer, a second trace 1404 corresponds to a middle point onthe wafer and a third trace 1406 corresponds to an edge point on thewafer. The traces are computer-generated according to a simulation basedon the shape of the zones and the relative movement between the waferand the zones. In addition to the actual path of a wafer point relativeto the electrode zones, the time spent affected by each zone isdetermined according to the simulation by accounting for the relativerotation speeds of the platen and head, the sweep range and frequencyand the location of obstructions (e.g., contact element) between thewafer points and the electrodes. The fraction of time spent by a point,j, in front of a counter-electrode, i, is denoted p_(ij).

One graphical representation of the time spent in the various zones isgiven in FIG. 15. In particular, three curves represent the time spentby various points on a diameter of the wafer in three separate zones: acentral zone, a middle zone, and an edge zone. The zones were defined byconcentric electrodes arranged similarly to those shown in FIG. 4. Thewafer points are represented on the x-axis (in this illustration thewafer was a 300 mm wafer) and the percent of the total time a pointspent in a given zone is represented on the y-axis. A first curve 1500represents the time wafer points spent in the central zone, a secondcurve 1502 represents the time wafer points spent in the middle zone anda third curve 1504 represents the time wafer points spent in the edgezone. Note that although points in a central part of the wafer (e.g.,between about −50 mm and +50 mm) may spend their entire time in thecenter zone, the first curve (corresponding to the center zone) does notreach 100 percent. This characteristic is due to obstructions to thepoints' view of the electrode which defines the center zone. As notedabove, a point may only experience a bias when disposed over aperforation in the polishing pad, thereby giving the point a view to theelectrode. Further, a point's view may be periodically obstructed by acontact element on the polishing pad.

Process Model Generation

The empirically determined charge-removal relationship and thetrajectory simulation are combined to relate to charge in each zone tothe removal at each wafer point. Based on the trajectory simulation, theaverage area of the wafer, A_(i), affected by the i^(th)counter-electrode can be determined. Assuming that the current densityis uniform across a zone, i.e., that the voltage drop across the waferis negligible, the charge-removal relationship in any given zone, R_(i),can be computed as follows:R _(i) =a*A _(w) /A _(i) *C _(i) +b   (Equation 1)In Equation 1, a is the slope the mathematical expression of therelationship between charge and removal, A_(w) is the plated area of thewafer, C_(i) is the charge of the i^(th) electrode and b is theintercept of the mathematical expression of the relationship betweencharge and removal.

The removal at each point becomes the average of the removal of eachzone weighted by the amount of time the point spent in front of eachzone, as given by:R _(j)=sum(i)(p _(ij) R _(i))   (Equation 2)

The process model described above can be summarized in the form of atransfer function taking as input the charge in each zone, C, andgenerating as output the removal profile R (i.e., the profile of thematerial to be removed). The charge in each zone, C, is represented by avector with N components, where N is the number of zones. The removalprofile, R, is represented by a vector with n components, where n is thenumber of sample points chosen on the wafer. Based on the process modeldescribed above, the transfer function is essentially linear and can bewritten as:R=AC+B,   (Equation 3)where A is a n×N matrix and A_(ij)=p_(ij)(a*A_(w)*A_(i)), and B is a(n×1) vector and Bi=b. Thus, the transfer function relates the removalprofile to the charge per zone (i.e., the charge read on each channel ofthe power supply).

It is noted that the process model described above is a “physical” modelin that the model accounts for physical parameters in a simulation.However, the process model 602 may be generated in a variety of ways.For example, the model 602 may be a statistical model based oncalibration wafers (i.e., the best fit based on x charges, where x isthe number of zones).

In any case, the process model 602 calculates a target charge per zone.If Pin is the incoming profile (provided by the profile measurementstation 102) and the Pdes is the desired profile, the process model 602can implement an optimization with respect to the achievable profile. Inone embodiment the optimization is a least square interpolation.Although the optimization may not be uniquely described, specificimplementations are contemplated. For example, one optimization is tominimize the standard deviation between the final profile, Pfin, and thedesired profile, Pdes. This optimization may be described as: minimizestddev(Pin-(AC+B)-Pdes). Another optimization is to minimize the maximumdeviation between Pfin and Pdes. This optimization may be described asminimize maxdevPin-(AC+B)-Pdes). Using such approaches (and others whichwill be recognized by those skilled in the art) the optimal values forthe target charges per zone can be determined prior to processing awafer. The power supplies for the respective zones are then controlledto ensure that the target charges are reached.

EXAMPLE

A counter-electrode assembly, such as the counter-electrode assembly 209was divided into five zones: an inner zone, an inner-central zone, acentral zone, an outer-central zone and an outer zone (Z1, Z2, Z3, Z4and Z5) respectively. The zones were arranged in a concentric circularmanner similar to the zones depicted for the electrode assembly 209shown in FIG. 4. Each of the zones was capable of receiving a separatebias with respect to a material layer of a wafer to be polished. Onehundred twenty one points, representing a broad sampling of variouslocations on the material layer were selected. A pre-determined set ofinstructions (i.e., a polishing program) that encoded a sequence ofrelative motion between the counter-electrode (as well as the polishingarticle) and the material layer of a wafer to be processed was providedto a computer (e.g., the computer 106). An algorithm based on thepolishing program was used to determine the sequence of relativepositions between the material layer and the individualcounter-electrodes of the electrode assembly as a function of timethroughout the polishing process. The algorithm calculated the locationof each point relative to the five zones of the counter-electrodes foreach of a total of 2400 instants in time (time steps). The algorithmalso calculated the number of time steps each point was associated witheach of the five zones (e.g., the number of times the point would befacing or under each of the zones). For a first order approximation, itis assumed that for embodiments in which the process cell comprises apad, a point on the material layer only experiences a bias when facing aperforation in the pad. It is also, assumed that a point does notexperience a bias when directly below a contact element on the pad(i.e., when the point's view of an opposing electrode is obscured by acontact element).

Based upon the program to be used to polish the material layer, thealgorithm determined that a first point in the center of the materiallayer was associated with Z2 for 1080 time steps (i.e. 45% of the totalnumber of time steps), associated with Z1, Z3, Z4, Z5 for 0 time steps,and associated with none of the zones (i.e., the point was not under aperforation in the pad and/or the point was under a contact element, andtherefore zero bias was experienced by the point) for the remaining 1320time steps. Therefore, for 45% of time, point A was associated with Z2,and the expected removal would be 0.45×R2, where R2 is the total removalcontributed by Z2.

From the algorithm it was further determined that a second point B, awayfrom the center of the material layer) was associated with Z2 for 570time steps (or 23.75% of the total number of time steps), associatedwith Z3 for 774 time steps (or 32.35% of the total number of timesteps), and associated with no zones for 1056 time steps. The expectedremoval for point B is therefore given by an average of the removals forZ1, Z2, Z3, Z4, and Z5, weighted by the percentage of the time spent ineach zone. Expressed in mathematical terms, the expected removal forpoint B is given by the mathematical expression,[0.2375×R2]+[0.3235×R3], where R3 is the total removal contributed byZ3.

The algorithm further calculated the expected removal rate for theremainder of the 121 points on the material layer in a similar manner.Specifically, for each point an expected removal rate was calculated as[P1×R1]+[P2×R2]+[P3×R3]+[P4×R4]+[P5 X R5]. P1, P2, P3, P4, and P5 arethe percentages of time that the particular point was associated withthe zones Z1, Z2, Z3, Z4, and Z5 respectively.

The material layer to be polished had a non-uniform initial profile,Pin. A desired removal profile, Rdes, was calculated as Pin−Pdes, wherePdes is the selected desired profile. A least-squares regression wasperformed to optimize the values for R1, R2, R3, R4, and R5 such thatthe actual removal profile, Ract, of the material layer after polishingwould closely match the desired removal profile, Rdes. The optimalbiases to be applied to each of the zones was then determined using apre-determined (linear) relationship between removal and charge. Theresultant removal profile was similar to the desired removal profile.

CONCLUSION

In various embodiments, advantages in electro-processing may beachieved. In some cases, these advantages may be substantialimprovements over the prior art. Some of these advantages are nowdescribed. However, whether or not an embodiment achieves an advantageand whether or not such an advantage may be considered a substantialimprovement is not limiting of the invention. Therefore, the advantagesdescribed below do not define or limit the invention, which is limitedonly by the claims that follow.

In one aspect, calibration requirements are eliminated. Conventionally,thickness measurement is performed by eddy current probes. The eddycurrent probe measures a current and then correlates the measured valueto thickness. In order to ensure accurate measurements the probe must becalibrated for pad wear and changes between different wafer types. Suchcalibration requirements may be eliminated by some embodiments of theinvention. As a result, successful process monitoring and endpointdetection according to embodiments of the invention are independent ofpad wear.

In another aspect, good spatial resolution is achieved. Spatialresolution using eddy current probes is limited to the width of theprobe (e.g., ¼ inch). Because embodiments of the invention do not relyon such intrusive devices, superior resolution is achieved.

In another aspect, embodiments of the invention are not restricted towafers having a minimal thickness. In contrast, eddy current probes arelimited in their ability to provide accurate measurements forthicknesses less than, for example, 2000 angstroms.

In another aspect, thickness measurements are not corrupted byinterference from other metal levels on a wafer. In contrast, adjacentmetal levels can interfere with measurements taken by eddy currentprobes.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1-24. (canceled)
 25. A method of determining removal of material from aplurality of points on a wafer, the removal being effected at least inpart by electro-chemical activity, the method comprising: determiningtrajectories for a plurality of points on a wafer relative to aplurality of electrodes each capable of being separately biased atdifferent bias levels during electrochemical processing; based on thetrajectories, determining an amount of time each of the plurality ofpoints spends being affected by each of the electrodes; based on thetrajectories and a predetermined charge-removal relationship relatingcharge removed to amount of material removed from the wafer, determiningan average amount of material removed from the wafer as effected by eachof the electrodes; and for each point of the plurality of points on thewafer, calculating an amount of material removed at the point as the sumof the average amounts of material removed from the wafer as effected byeach of the electrodes weighted by the corresponding amount of timespent being affected by the respective electrode.
 26. The method ofclaim 25, wherein determining the trajectories comprises accounting fora construction of a processing cell housing the electrodes.
 27. Themethod of claim 26, wherein accounting for the construction of theprocessing cell comprises accounting for process parameters andconstruction geometry.
 28. The method of claim 27, wherein accountingfor process parameters comprises accounting for a relative motionbetween the wafer and the plurality of electrodes.
 29. The method ofclaim 27, wherein accounting for process parameters comprises accountingfor a rotation speed of a polishing pad, a rotation speed of a wafercarrier retaining the wafer during processing, and a sweep range andfrequency of the wafer carrier relative to the polishing pad.
 30. Themethod of claim 27, wherein accounting for construction geometrycomprises accounting for a shape of the electrodes and a location ofcontact elements disposed on a wafer polishing pad, the contact elementsbeing a counter electrode for the plurality of electrodes.
 31. A methodof electro-processing a wafer, comprising: providing an electrodeassembly comprising at least two separately biased electrodes; providinga process model which relates a charge for each of the electrodes to anamount of material removed at each of a plurality of points on a waferon the basis of a predetermined trajectory of the plurality of pointsrelative to the electrodes and a predetermined charge-removalrelationship which relates charge removed to amount of material removedfrom the wafer; for a specified desired profile of the wafer,determining a target charge for each electrode according to the processmodel; moving the wafer relative to the electrodes according to thepredetermined trajectory of the plurality of points; and terminatingeach bias to the respective electrode upon reaching the respectivetarget charge.
 32. The method of claim 31, wherein the process modelaccounts for an amount of time each point is affected by each electrodebased on the predetermined trajectory.
 33. The method of claim 31,wherein the process model accounts for a construction of a processingcell housing the electrodes.
 34. The method of claim 31, wherein theprocess model accounts for process parameters and a constructiongeometry of a processing cell housing the electrodes.
 35. The method ofclaim 34, wherein accounting for process parameters comprises accountingfor a relative motion between the wafer and the plurality of electrodes.36. The method of claim 31, further comprising providing a polishing padand wherein moving the wafer relative to the electrodes according to thepredetermined trajectory comprises mechanically polishing the wafer onthe polishing pad.
 37. The method of claim 36, wherein the predeterminedtrajectory accounts for a rotation speed of the polishing pad, arotation speed of a wafer carrier retaining the wafer during processing,and a sweep range and frequency of the wafer carrier relative to thepolishing pad.
 38. The method of claim 36, wherein the polishing padcomprises contact elements defining a counter-electrode to the at leasttwo electrodes and wherein the process model accounts for a shape of theelectrodes and a location of contact elements. 39-57. (canceled)